The reduction in the size of planar antennas is a major issue in making them easier to use and to incorporate in modem systems.
The basic principle of most of the solutions implemented hitherto consists in increasing the equivalent electrical length of the printed pattern, so that it can radiate at the required frequency, while reducing its physical dimensions (i.e. its surface or its volume).
To this end, the most commonly used structures correspond to:                patch type solutions with inscribed slots, these slots allowing the electrical path of the signal to be elongated over the planar pattern (see for example patent documents WO 01/31739 and WO 01/17063), or        solutions for which the radiating pattern is folded back so as to gain in compactness (see for example patent documents WO 02/052680, WO 01/63695 and U.S. Pat. No. 6,483,462 B2).        
It should be noted that these different concepts may also be combined within one and the same structure (see for example patent document WO 02/101874).